1. [Field of the Invention]
The present invention relates to a positioning device including a servomotor and, more particularly, to a servomotor speed control system in a positioning device included in, for example, a type wheel positioning system in a printer, a carriage positioning system in a printer, or a machine tool.
2. [Description of the Prior Art]
In a positioning device, a servomotor is normally held in a halt state at a predetermined position. When a positioning commmand is applied to the positioning device, the servomotor is accelerated to the maximum speed, and rotates at the maximum constant speed toward a target point. When the servomotor position becomes close to the target point, the servomotor is decelerated so that the motor rotation is stopped precisely at the target point. That is, the servomotor speed must be controlled with reference to the distance between the current motor position and the target point. A preferred motor speed V is determined in accordance with the following formula. EQU V=a.sqroot.S
where, a is a constant determined by the motor characteristics and the load connected to the servomotor, and S is the distance between the current motor position and the target point.
In a conventional system, an arithmetic calculation circuit is employed in a positioning device, which calculates a preferred motor speed upon every detection of the current motor position. The calculation can not track the high speed rotation because of the complicated radical operation.
In order to accurately track the high speed rotation, another positioning device is proposed, wherein a ROM table is provided in a control system for determining a preferred motor speed. In this system, the ROM table stores a preferred motor speed for each of the distance between the current motor position and the target point. The distance is scaled to correspond to the unit of the position detection output developed from the position detection device. Therefore, a considerably large capacity is required for the ROM table.